This invention relates to improvements in an electric discharge machining method and apparatus for performing machining (rocking machining) while rocking an electrode with respect to a workpiece in a plane vertical to a machining feed direction.
Rocking machining is intended for efficiently ejecting work scrap with stirring by performing electric discharge machining to a workpiece while moving an electrode relatively with respect to the workpiece in a plane vertical to a machining feed direction. Also, simple shapes such as circle or rectangle are generally used as a rocking shape, and the shape similar to an electrode shape is obtained as the shape after machining the workpiece.
Such rocking machining includes means for performing constant-speed rocking with a constant swing speed, means for controlling the amount of electrode transfer according to an interelectrode voltage between an electrode and a workpiece as disclosed in JP-A-6-126540, means for controlling the amount of electrode transfer by the amount of residual machining calculated from a difference between an electrode position and a target machining shape as disclosed in JP-A-2-212026, and so on.
Also, there is means for dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether a target machining shape is attained every each division shape and completing the rocking machining when the rocking movement completion determination is made in all the division shapes, and such a machining method is disclosed in JP-A-2-212026, JP-A-6-126540, JP-A-10-166224, and so on.
In a method using an interelectrode voltage for a change in a swing speed, it is necessary to detect the interelectrode voltage during machining and predetermine the amount of electrode transfer based on interelectrode voltage data. Thus, an apparatus for detecting and calculating the interelectrode voltage and data of the amount of electrode transfer based on the interelectrode voltage data must be provided. Also, in constant-speed rocking, in the case of dividing a rocking shape and making a rocking completion determination, it becomes a constant swing speed even within the division shape in which a target shape has been attained and the rocking completion determination has been made, so that waste time increases. Further, in the constant-speed rocking, when a factor which deteriorates properties of a machined surface of abnormal electric discharge due to an electric discharge concentration or a short circuit etc. or secondary electric discharge performed through work scrap and so on occurs, the rocking is performed at the constant swing speed, so that continuous time of abnormal electric discharge etc. is the same at all the positions and it is difficult to break the continuation of the abnormal electric discharge etc. by rocking movement, with the result that machining tends to become unstable.
FIG. 7 is a diagram showing rocking paths, and as shown in FIG. 7A, there is a rocking path for performing machining by a predetermined amount of rocking after movement from the rocking coordinate origin to the X-axis positive direction and as shown in FIG. 7B, there is a rocking path for performing machining by a predetermined amount of rocking after movement from the rocking coordinate origin to a direction of 45xc2x0 (for example, it is assumed that a counterclockwise direction is positive.) with respect to the X-axis positive direction. Also, FIG. 8 is a diagram showing dividing examples of a rocking shape, and since a division is started on the X-axis of the rocking coordinates in the division of a conventional rocking shape, when the rocking shape is equally divided into n portions, there are a case of dividing one quadrant into an even number as shown in FIG. 8A and a case of dividing one quadrant into an odd number as shown in FIG. 8B. A division expression of such a division is given by N=xcex8/360xc3x97S (where digits to the right of the decimal point are discarded) when it is assumed that the number of the division shape is N (N=0, 1, 2. . . , nxe2x88x921) and an angle of an electrode position viewed from the rocking coordinate origin is xcex8 (the X-axis positive direction is xcex8=0xc2x0) and the number of divisions of the rocking shape is S. In the case of making a completion determination every each division shape, depending on the number of divisions (for example, the case of equally making an even-numbered division in multiples of 8), when the completion determination is made at A1 and A2 of adjacent division shapes in a corner portion of a target machining shape of a workpiece as shown in FIG. 9, a large left section occurs in this corner portion and shape accuracy becomes worse. Also, in rocking machining of an elongated electrode shape as shown in FIG. 10A, a difference in a machining area per each division shape becomes large and as shown in FIG. 10B, two division shapes are used in the center of each side of a target machining shape of a workpiece, so that a large left section occurs and shape accuracy becomes worse when a completion determination is made, for example, at A3 and A4 as shown in FIG. 10B.
FIG. 11 is an illustration showing a division example of a rocking shape in rocking machining capable of switching a swing speed every division shape, and in such rocking machining, the swing speed is determined on the basis of the amount of residual machining calculated from a difference between a target machining shape and the present electrode position and a high swing speed (for example, V1 of FIG. 11) is given when a left section is small and a low swing speed (for example, V2 of FIG. 11) is given when a left section is large. Also, in the case that an electrode moves from a division shape in which the high swing speed V1 is given to a division shape in which the low swing speed V2 is given, when the speed difference between the high swing speed V1 and the low swing speed V2 is large, the electrode reaches the inside of the division shape in which the low swing speed V2 is given at the high swing speed V1 due to a delay etc. of calculation time. Therefore, in such a case, a left section tends to occur, so that shape accuracy becomes worse and further machining time becomes long.
This invention is implemented to solve the problems described above, and an object of the invention is to obtain an electric discharge machining method and apparatus capable of improving machining shape accuracy and reducing machining time in the electric discharge machining method and apparatus with high machining stability of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes.
With an electric discharge machining method according to a first invention, in the electric discharge machining method of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes, the rocking shape is divided so that either one or both of each corner and the center of each side of the target machining shape is located on a bisector or substantially a bisector of a division angle.
With an electric discharge machining method according to a second invention, in the electric discharge machining method of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes, the rocking shape is divided while changing a division angle.
With an electric discharge machining method according to a third invention, in the electric discharge machining method according to the second invention, the rocking shape is divided so that the division angle becomes smaller with an approach to each corner of the target machining shape.
With an electric discharge machining method according to a fourth invention, in the electric discharge machining method of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes, a first swing speed calculated from the amount of residual machining at the time of swing before one round in a first division shape which is any one of the division shapes is compared with a second swing speed calculated from the amount of residual machining at the time of swing before one round in a division shape forward by a predetermined number of divisions before the first division shape is reached, and when a value of (the second swing speed minus the first swing speed) exceeds a predetermined standard and is large, the swing speed is reduced from the division shape forward by the predetermined number of divisions and an electrode is moved to the first division shape.
With an electric discharge machining apparatus according to a fifth invention, in the electric discharge machining apparatus having a function of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes, there is provided a rocking shape division part having a function of dividing the rocking shape so that either one or both of each corner and the center of each side of the target machining shape is located on a bisector or substantially a bisector of a division angle.
With an electric discharge machining apparatus according to a sixth invention, in the electric discharge machining apparatus having a function of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes, there is provided a rocking shape division part having a function of dividing the rocking shape while changing a division angle.
With an electric discharge machining apparatus according to a seventh invention, in the electric discharge machining apparatus according to the sixth invention, the rocking shape division part has a function of dividing the rocking shape so that the division angle becomes smaller with an approach to each corner of the target machining shape.
With an electric discharge machining apparatus according to an eighth invention, in the electric discharge machining apparatus having a function of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes, there are provided a residual machining amount calculation part having a function of calculating the amount of residual machining from a difference between the target machining shape and the present electrode position, and a rocking movement control part having a function of setting the swing speed using swing speed data previously prepared from the amount of residual machining calculated from the residual machining amount calculation part and a function of comparing a first swing speed calculated from the amount of residual machining at the time of swing before one round in a first division shape which is any one of the division shapes with a second swing speed calculated from the amount of residual machining at the time of swing before one round in a division shape forward by a predetermined number of divisions before the first division shape is reached and reducing the swing speed from the division shape forward by the predetermined number of divisions and moving an electrode to the first division shape when a value of (the second swing speed minus the first swing speed) exceeds a predetermined standard and is large.
This invention has the following effects since the invention is constructed as described above.
The first invention and the fifth invention have an effect capable of reducing a left section and improving machining shape accuracy higher.
The second invention and the sixth invention have an effect capable of obtaining a division shape according to required shape accuracy or required machining time, and so on.
The third invention and the seventh invention have an effect capable of reducing a left section of the corner and improving machining shape accuracy higher.
The fourth invention and the eighth invention have an effect capable of reducing a left section and improving machining shape accuracy. Further, the inventions have an effect capable of reducing machining time.